Mars-crosser

An asteroid whose perihelion
lies within part or all of the orbit of Mars. Mars-crossers
are subdivided into shallow Mars-crossers, with perihelia
between 1.58 and 1.67 AU, and deep Mars-crossers, with
perihelia between 1.3 and 1.58 AU; by comparison the distance of Mars from
the Sun varies between about 1.38 and 1.67 AU. Mars-crossers are believed
to have originated as main-belt asteroids that fell into a 3:1 orbital
resonance (at a heliocentric distance of 2.5 AU) with Jupiter.
Objects that go around the Sun three times for every orbital period of Jupiter
meet up with the giant planet at the same point every third orbit. Jupiter's
powerful gravity then perturbs the asteroid's path, increasing its eccentricity
with each encounter. Over a period of about 100,000 years, as perturbations
accumulate, the asteroid becomes a Mars-crosser. Further perturbations from
Mars, over a much longer period of several tens of million years, can then
transform the asteroid into an Earth-crossing
asteroid – and a potential hazard.